Annual shooting bags were considered as a random population sample. Shooting took place from mid-September to late November in P1 and P2, and during October–November in CM and CH (i.e. always after the breeding season). Data from animals shot were collected in 1993–99 in CM, 1994–99 in CH and in 1996–99 in P1 and P2. The eyes of every collected hare were kept in 10% formalin and female uteri were frozen. Animals were aged by the eye-lens mass technique: from a standard curve (Broekhuizen & Maaskamp 1979) hares were classified as adults or young of the year, for which bimonthly cohorts were established according to the estimated date of birth. The following analyses were undertaken on all sites individually. The age structure was defined as the proportion of young in the sample. The proportion of breeding females (i.e. those having delivered at least one litter) and fecundity data were estimated by placental scar analysis, a method based for the detection and classification of embryo implantation sites on uterine walls late in the breeding season (Bray et al. 2003). As scars fade over winter, those seen in animals shot in autumn represent all breeding in the preceding breeding season and none from the season before. Implantation sites were counted to estimate last breeding-season's production, then pooled by visual similarities to define litter numbers and sizes. Because the limited sample sizes did not allow the analysis of yearly variations within each site the data were pooled over years by population trend.
Leveret survival was estimated by comparing age structures to fecundity data. Let PYi be the proportion of young in the shooting bag from study site i, then the number of young per adult in the bag is PYi/(1 − PYi) (equation 1). The adult sex ratio is likely to be imbalanced because males usually survive better than females: let k be the ratio of sex-dependent annual survival rates (k = SYm/SYf = 0·50/0·40 in yearlings, then SAm/SAf = 0·55/0·50 in adults, model 13 in Marboutin & Hansen 1998) and let nt = (SM)t + (SF)t, with t= 1, 2, 3, … , n years. The adult asymptotic sex ratio was calculated from a horizontal life table convergence, based on simulated annual cohorts of yearlings and adults, as lim.(Σktnt)/Σnt = 1·41. Let PBFi be the proportion of breeding females in population i, then the number of young per breeding female in bag i is NYi = [PYi/(1 – PYi)] × (1 + 1·41)/PBFi (equation 2), to be weighed next for female survival during the time elapsed between the breeding chronology median and the opening of the shooting season (mi = 3, 4, 3·5, 3 and 2·5 months, respectively, in CM, CH1, CH2, P1, P2). The resulting number of surviving young per female then alive is (equation 3), with an averaged monthly survival rate φi = [0·40 × PYi + 0·50 × (1 − PYi)]1/12 to account for the mothers’ age structure (yearling, adult). Let Fi be doe fecundity, and the intuitive leveret survival index is NY′i/Fi. Young females that bred between birth and the shooting season, however, produced some young in the bag. By eye-lens mass, we defined five bimonthly age classes among the PYi leverets (i.e. those born in January–February, March–April, etc.). Let ACi,j be the frequency of age class j in population i, and PBYi,j the corresponding proportion of breeding young females, and let fi be their fecundity (independent of age class). The contribution of young females relative to adults, could roughly be estimated as Ci = [(fi × PYi/2) ×Σ(ACi,j × PBYi,j)]/[Fi × (1 − PYi) × PBFi/(1 + 1·41)] (equation 4). The leveret survival index therefore is (equation 5).